DISEASE CHARACTERISTICS: Diagnosis of chronic phase chronic myeloid leukemia (CML) by cytogenetic and/or molecular analyses No more than 10% blasts on blood and bone marrow morphology Philadelphia (Ph) chromosome positive Ph chromosome-negative CML allowed if evidence of the BCR-ABL rearrangement by molecular or FISH analyses or evidence of the P120 protein Duration of CML less than 3 years, unless cytogenetic remission to interferon has been achieved Failed to obtain and maintain a complete cytogenetic remission on a prior trial of interferon therapy Absence of detectable PH-negative cells in bone marrow or blood after 6 months of therapy Lack of a progressive increase in Ph-negative cells between 6 and 12 months of therapy Less than 50% Ph-negative cells after 12 months of therapy Absence of complete cytogenetic remission after 24 months of therapy Inability to tolerate prior interferon therapy No accelerated phase or blast crisis CML, chronic myelomonocytic leukemia, or juvenile CML Concurrent enrollment on the busulfan and cyclophosphamide preparative regimen protocol